Topic: I Dont like it but i have to do it

I need to open access to a no username and password to my application.

What i did was i added a userkey field on my users model that can be past via a get or post method from another site.
that will then find the correct user and log them in as if they had put in there user name and password.

Now i am using device to log in my users. but i am not sure where to append the second login method.

in my user controller i have

def login_bypass
    id = params[:id]
    @u = User.find_by_key(id)                                                                                                        
    if @u == nil
      flash[:error] = t(:please_contact_support)                                                                                                 
      redirect_to login_path                                                                                                                
    else                                                                                                                                    
        // device log in with @u info 
      flash[:success] = t(:welcome_to_the_site)
      redirect_to users_path                                                                                                               
    end
  end  

any one know how should i go on?